Semiconductor device

ABSTRACT

An object of the present invention is to obtain a semiconductor device having highly reliable bonding portions. The semiconductor device according to the present invention includes an insulating substrate on which a conductive pattern is formed, and an electrode terminal and a semiconductor element which are bonded to the conductive pattern, the electrode terminal and the conductive pattern are bonded by ultrasonic bonding on a bonding face, and the ultrasonic bonding is performed at a plurality of positions.

TECHNICAL FIELD

The present invention relates to a semiconductor device, particularly to a semiconductor device to which an electrode terminal is bonded by ultrasonic bonding.

BACKGROUND ART

Nowadays, power semiconductor devices are necessary equipment in many different fields from small-sized electronic devices to automobiles, bullet trains, etc., and also to electric power transmission and distribution. The use areas and application fields have been increasing year by year, and in the fields of automobiles, bullet trains, electric power, and the like, higher current, higher breakdown voltage, and operation temperatures in a wide range, especially durability under high operation temperatures have been desired, not to mention high reliability and long lifetime. Since conventional solder-bonding techniques cannot ensure reliability of soldering materials under high temperatures, it is becoming more and more difficult to fabricate the elements that satisfy the conditions. As one of bonding techniques to solve this problem, the ultrasonic bonding has been introduced.

Here, a semiconductor device in which a conductive pattern is formed on a surface of an insulating substrate, and a semiconductor element and an electrode terminal are bonded to the conductive pattern is considered. Conventionally, the electrode terminal and the conductive pattern are subjected to the ultrasonic bonding at one position. When a power semiconductor element is used under conditions of high temperatures for a long period of time, a thermal stress is generated due to a difference in thermal expansion coefficients between the electrode terminal and the insulating substrate on which the conductive pattern is formed, and a bonding portion sometimes peels off.

In addition, as the semiconductor device carries larger current, it becomes necessary to increase a cross-sectional area of the electrode terminal. In other words, an increase in the thickness or the width of the electrode terminal requires an increase in the size of the electrode terminal. The increase in size of the electrode terminal causes an increase of the stiffness of the terminal. This results in an increase of a stress applied to the bonding portion accompanied by displacement of a package due to the heat generated by operation of the power semiconductor element, and thus a problem, such as reduction of bonding strength and terminal peeling, may occur.

Further, due to an increase in the thickness of the electrode terminal and the area of a bonding face, it becomes harder to propagate the energy of the ultrasonic bonding to the bonding face. To increase the bonding strength of the ultrasonic bonding, a bonding load and an ultrasonic output are generally increased as a countermeasure. However, the increase of these elements may cause a problem, i.e., the insulating substrate provided under the conductive pattern is damaged.

Accordingly, Patent Document 1 discloses a technique in which slits are provided at a plurality of positions between signal terminals that are subjected to the ultrasonic bonding, so that the ultrasonic bonding is stably performed. In addition, Patent Document 2 discloses a technique in which the ultrasonic bonding is performed at a plurality of positions between metal ribbons and electrode pads on a semiconductor chip to increase the area of the bonding face.

PRIOR ART DOCUMENTS Patent Documents

Patent Document 1: Japanese Patent Application Laid-Open No. 2010-10537

Patent Document 2: Japanese Patent Application Laid-Open No. 2012-146747

SUMMARY OF INVENTION Problems to be Solved by the Invention

However, the above conventional arts include the following problems to be solved. Although an initial bonding strength can be sufficiently obtained by the technique according to Patent Document 1, the bonding is susceptible to a thermal stress caused by heat from an electrode accompanied by use of a semiconductor module. As a bonding part of the electrode is divided by a slit and each of the parts is presumably bonded at one position, the plurality of bonding portions may all peel off due to generation of the stress.

According to Patent Document 2, an integral metal ribbon is bonded by ultrasonic bonding at a plurality of portions, but an unbonded portion between the bonded portions is floated from a target element and forms a gap. This is because a bonding target is a ribbon, which is thin in a thickness normally equal to or less than 300 μm, and the ribbon may split without a gap. The bonding target according to the present invention is an electrode having the thickness of 0.5 mm or more and hardly split, and thus it is not necessary to provide a gap.

The present invention has been made to solve the above problems, and an object is to obtain a semiconductor device having highly reliable bonding portions.

Means for Solving the Problems

The semiconductor device according to the present invention includes an insulating substrate on which a conductive pattern is formed, and an electrode terminal and a semiconductor element that are bonded to the conductive pattern, the electrode terminal and the conductive pattern are bonded together by the ultrasonic bonding through at least one bonding face, and the ultrasonic bonding is performed at a plurality of positions.

In addition, the semiconductor device according to the present invention includes an insulating substrate on which a conductive pattern is formed, and an electrode terminal and a semiconductor element that are bonded to the conductive pattern, the electrode terminal and the conductive pattern are bonded together by the ultrasonic bonding through at least one bonding face, the electrode terminal includes a projection and the conductive pattern includes a depression on the bonding face, alternatively the electrode terminal includes a depression and the conductive pattern includes a projection on the bonding face, and the projection and the depression are engaged with each other.

Effects of the Invention

In the semiconductor device according to the present invention, a plurality of ultrasonically bonding portions are provided on the bonding face. With this structure, an area of each bonding portion can be reduced. As a result, an absolute value of a thermal stress applied to each bonding portion can be reduced, and thus peeling of the bonding face can be suppressed. In addition, since the total area of the bonding portions increases, a reliable semiconductor device can be obtained.

Moreover, in the semiconductor device according to the present invention, the projection and the depression are fit with each other before performing the ultrasonic bonding, thereby facilitating positioning of the electrode terminal with respect to the conductive pattern. With this structure, at the time of performing the ultrasonic bonding, the relative position between the electrode terminal and the conductive pattern is settled, and the energy of the ultrasonic bonding can be sufficiently obtained. Since the ultrasonic bonding can be stably performed, a semiconductor device having a high bonding reliability can be obtained.

The object, features, aspects, and advantageous effects of the present invention are clarified by the following detailed description and the accompanied drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a plan view and a sectional view of a semiconductor device according to a first embodiment.

FIG. 2 is a perspective view of an electrode terminal and a conductive pattern of the semiconductor device according to the first embodiment.

FIG. 3 is a perspective view of an electrode terminal and a conductive pattern of a semiconductor device according to a second embodiment.

FIG. 4 is a perspective view of an electrode terminal and a conductive pattern of a semiconductor device according to a third embodiment.

FIG. 5 is a perspective view of an electrode terminal and a conductive pattern of a semiconductor device according to a fourth embodiment.

FIG. 6 is a plan view and a sectional view of a semiconductor device according to a fifth embodiment.

FIG. 7 is a perspective view of an electrode terminal and a conductive pattern of the semiconductor device according to the fifth embodiment.

FIG. 8 is a perspective view of an electrode terminal and a conductive pattern of a semiconductor device according to a sixth embodiment.

FIG. 9 is a perspective view of an electrode terminal and a conductive pattern of a semiconductor device according to a seventh embodiment.

FIG. 10 is a perspective view of an electrode terminal and a conductive pattern of a semiconductor device according to an eighth embodiment.

FIG. 11 is a perspective view of an electrode terminal and a conductive pattern of a semiconductor device according to a ninth embodiment.

FIG. 12 is a sectional view of the electrode terminal and the conductive pattern of the semiconductor device according to the ninth embodiment.

FIG. 13 a plan view and a sectional view of a semiconductor device according to a tenth embodiment.

FIG. 14 is a sectional view of a semiconductor device according to a prerequisite art.

FIG. 15 is a plan view of the semiconductor device and a sectional view of an electrode terminal according to the prerequisite art.

FIG. 16 is a perspective view of the electrode terminal and a conductive pattern of the semiconductor device according to the prerequisite art.

DESCRIPTION OF EMBODIMENTS

<Prerequisite Art>

Before describing embodiments of the present invention, a prerequisite art for the present invention is described below. FIG. 14 is a sectional view of a semiconductor device (power module) according to the prerequisite art. The semiconductor device according to the prerequisite art includes an insulating substrate 1 or an insulating sheet, a Metal Oxide Semiconductor Field Effect Transistor (MOSFET) chip 2, a Shottkey Barrier Diode (SBD) chip 3, conductive patterns 4 a, 4 b, an electrode terminal 6, a wire 14, a sealing member 9, an outsert case 10, and a base plate 11.

The insulating substrate 1 is bonded to the base plate 11 for heat dissipation through a bonding member 8. The conductive patterns 4 a, 4 b formed from a conductive material are provided on the insulating substrate 1. The MOSFET chip 2 and the SBD chip 3 are mounted on the conductive pattern 4 a with the bonding member.

The electrode terminal 6 is bonded to the conductive pattern 4 b on the bonding face 7. The electrode of the MOSFET chip 2 and the electrode of the SBD chip 3 are bonded with each other by the wire 14. In addition, the electrode of the SBD chip 3 and the conductive pattern 4 b are bonded with each other by the wire 14.

The outsert case 10 is attached to the base plate 11 by an adhesive agent 12. The outsert case 10 is filled with the insulating sealing member 9 formed of silicone gel, elastomer, or the like.

The conductive patterns 4 a, 4 b are formed by etching a copper plate brazed to the insulating substrate 1. The copper plate may be an aluminum plate. The surfaces of the conductive patterns 4 a, 4 b may be covered with nickel.

Although the insulating substrate 1 is formed by using an insulating material formed from AlN, the insulating material may also be Al₂O₃, Si₃N₄, or the like. Although the MOSFET chip 2 is mounted as a semiconductor element, the semiconductor element may also be an Insulated Gate Bipolar Transistor (IGBT). In addition, the SBD chips 3 may be a Free Wheel Diode (FWD). Note that the semiconductor element may be selected from elements having Si, SiC, or GaN as a base material. Although the wire 14 is an Al wire having 400 μm in diameter, the wire 14 may also be a wire formed from an Al alloy, a plate-shaped Al sheet, or a good conductive metal wire composed of Cu.

Although solder is generally used as the conductive bonding member 8, a sintered body of fine Ag particles having a diameter of about several nanometers may be used for coping with high-temperature operations. In addition, in the case of a semiconductor device handling a small current, a conductive adhesive agent containing a conductive filler may be used.

Although the insulating substrate 1 is bonded to the base plate 11 by the bonding member 8, the insulating substrate 1 may be formed integrally with the base plate 11. The material of the base plate 11 is a composite material formed from Al and ceramic, such as Al-SiC. In addition, the base plate 11 may also be a copper plate.

In FIG. 14, the bonding between the electrode terminal 6 and the conductive pattern 4 b is performed by soldering. The solder bonding requires controlling of the maximum operation temperature and the melting point of solder, and has difficulty in coping with elevation of operation temperatures in the case where an SiC element, which is operable at high temperatures, is mounted as a semiconductor element.

Accordingly, in recent years, ultrasonic bonding has been applied to the bonding between the electrode terminal 6 and the conductive pattern 4 b. The ultrasonic bonding is a technique in which ultrasonic vibration is applied to the bonding face of the materials that make contact with each other to generate frictional heat at a bonding portion, while imposing a load on the bonding face so that coupling metals are joined at the interface at an atomic level.

FIG. 15 is a view schematically showing the ultrasonic bonding. In addition, FIG. 16 is a perspective view of the bonding portion of the electrode terminal 6 and the conductive pattern 4 b. As shown in FIG. 15, a tool 13 is pressed against an upper part of the bonding face 7 between the electrode terminal 6 and the conductive pattern 4 b and is ultrasonically vibrated, for example in the direction of the arrow shown in the figure. The tool 13 transmits ultrasonic waves to the bonding face 7. At the time of the ultrasonic bonding, a recess 5 is formed on the upper surface of the electrode terminal 6 against which the tool 13 is pressed. Use of the ultrasonic bonding enables bonding in a short period of time without using a material such as an adhesive agent, solder, or the like. In addition, the use of the ultrasonic bonding also enables coping with high-temperature operations.

According to the prerequisite art, as shown in FIG. 16, the electrode terminal 6 and the conductive pattern 4 b are bonded together by the ultrasonic bonding at one position. When a power semiconductor element is used under high-temperature conditions for a long period of time, the bonding portion sometimes peels off because of a thermal stress caused by a difference in thermal expansion coefficients between the electrode terminal 6 and the insulating substrate 1 on which the conductive pattern 4 b is formed.

In addition, as the semiconductor device carries larger current, it becomes necessary to increase a cross-sectional area of the electrode terminal 6. In other words, an increase in the thickness or the width of the electrode terminal 6 requires an increase in the size of the electrode terminal 6. The increase in size of the electrode terminal 6 causes an increase of the stiffness of the terminal. This results in an increase of a stress applied to the bonding portion accompanied by displacement of a package due to the heat generated by operation of the power semiconductor element, and thus a problem, such as reduction of bonding strength and terminal peeling, may occur.

Further, due to an increase in the thickness of the electrode terminal and the area of a bonding face 7, it becomes harder to propagate the energy of the ultrasonic bonding to the bonding face 7. To increase the bonding strength of the ultrasonic bonding, a bonding load and an ultrasonic output are generally increased as a countermeasure. However, the increase of these elements may cause a problem, i.e., the insulating substrate 1 provided under the conductive pattern 4 is damaged.

First Embodiment

<Structure>

FIG. 1 is a plan view and a front view of a structure of a semiconductor device according to a first embodiment. FIG. 2 is a perspective view of an electrode terminal 6 and a conductive pattern 4 b. In this first embodiment, like in the prerequisite art (FIG. 14), conductive patterns 4 a and 4 b are disposed on the insulating substrate 1, and semiconductor elements (a MOSFET chip 2 and an SBD chip 3) are bonded to the conductive pattern 4 a. The electrode terminal 6 is bonded on the conductive pattern 4 b.

According to the prerequisite art, ultrasonic bonding is performed at only one position on one bonding face between the electrode terminal 6 and the conductive pattern 4 b. Accordingly, a recess 5 is formed by the ultrasonic bonding at one position on the upper surface of a bonding portion of the electrode terminal 6.

On the other hand, according to this first embodiment, as shown in FIG. 1, a plurality of bonding portions are provided on one bonding face 7 of the electrode terminal 6 to which the conductive pattern 4 b is bonded. Accordingly, a plurality of recesses 5 a, 5 b are formed by the ultrasonic bonding on the upper surface of the bonding portion of the electrode terminal 6. The bonding portions are spaced apart from each other. In other words, an interval of 50 μm or less is provided between the recesses 5 a and 5 b. Alternatively, the bonding portions may be in contact with each other.

<Operation>

In the semiconductor device configured as shown in FIG. 1, when a semiconductor element comes into operation, a current flows into the electrode terminal 6 and then the electrode terminal 6 generates heat. The generated heat causes the whole electrode terminal 6 to expand, a stress, such as tensile stress, is applied to the root of the electrode terminal 6 that is a bonding portion. In addition, the thermal stress is generated on the bonding face 7 between the electrode terminal 6 and the conductive pattern 4 b because of a difference in thermal expansion coefficients between the materials of the insulating substrate 1 and the electrode terminal 6.

<Effects>

The semiconductor device according to this first embodiment includes an insulating substrate 1 on which conductive patterns 4 a, 4 b are formed, and an electrode terminal 6 and a semiconductor element that are bonded to the conductive patterns 4 a, 4 b, the electrode terminal 6 and the conductive pattern 4 b are bonded together by the ultrasonic bonding through the bonding face 7, and the ultrasonic bonding is performed at a plurality of positions.

Accordingly, in this first embodiment, as shown in FIG. 1 and FIG. 2, a plurality of ultrasonically bonding portions are provided on the bonding face 7. With this structure, an area of each bonding portion can be reduced. As a result, an absolute value of a thermal stress applied to each bonding portion can be reduced, and thus peeling of the bonding face 7 can be suppressed. In addition, since the total area of the bonding portions increases, a highly reliable semiconductor device can be obtained.

In addition, the semiconductor device according to this first embodiment includes one bonding face 7, and the ultrasonic bonding is performed at a plurality of positions on the bonding face 7.

Accordingly, even with one bonding face 7, this first embodiment can provide a highly reliable semiconductor device by performing the ultrasonic bonding at two positions.

Second Embodiment

<Structure>

FIG. 3 is a perspective view of an electrode terminal 6 and a conductive pattern 4 b according to a second embodiment. In this second embodiment, the electrode terminal 6 is a flat plate. The root of the electrode terminal 6 is divided into two branches in the width direction. In other words, the root of the electrode terminal 6 includes two branches 6 a, 6 b.

As shown in FIG. 3, the branches 6 a, 6 b are bent to form an angle of 90° with each other in a plan view. The branch 6 a is bonded to the conductive pattern 4 b by ultrasonic bonding on the bonding face 7 a. In the same manner, the branch 6 b is bonded by the ultrasonic bonding to the conductive pattern 4 b on the bonding face 7 b. On the bonding faces 7 a, 7 b, the branches 6 a, 6 b are respectively bonded by the ultrasonic bonding to the conductive pattern 4 b at one position. Recesses 5 a, 5 b are formed by the ultrasonic bonding at the upper surfaces of the branches 6 a, 6 b.

<Operation>

In this second embodiment, the sectional areas of the branches 6 a and 6 b of the electrode terminal 6 are assumed equal to each other. In this case, when the current flowing in one electrode terminal is defined as I [A], the current flowing in each of the branches 6 a, 6 b is I/2 [A].

In addition, the area of the bonding face of each of the branches 6 a, 6 b is half of that of the bonding face according to the first embodiment. Accordingly, with respect to the mechanical stress due to the expansion of the electrode terminal 6, the stress applied to the branches 6 a, 6 b is also reduced by half.

<Effects>

The semiconductor device according to this second embodiment includes a plurality of bonding faces 7 a, 7 b, the root of the electrode terminal 6 is divided into branches, and the divided root (i.e., branches 6 a, 6 b) forms the plurality of bonding faces 7 a, 7 b, and each of the bonding faces 7 a, 7 b includes at least one position that is subjected to the ultrasonic bonding.

In this second embodiment, the root of the electrode terminal 6 is divided into two branches, and the branches 6 a, 6 b form two bonding faces 7 a, 7 b, respectively. Each of the bonding faces 7 a, 7 b includes one position that is subjected to the ultrasonic bonding. Accordingly, in this second embodiment, by dividing the root of the electrode terminal 6 into two branches, the current flowing in each terminal (branches 6 a, 6 b) becomes I/2 [A], and thus the heating value of each of the bonding faces is reduced by half as compared to that of the first embodiment. This enables the thermal stress applied to each bonding face to be reduced by half.

In addition, since two bonding faces 7 a, 7 b are provided, peeling of the bonding faces 7 a, 7 b can be suppressed as compared to a case where one bonding face 7 is provided as in the prerequisite art, even when a force to peel the electrode terminal 6 upward (stress generated perpendicular to the bonding face) is generated. Accordingly, a semiconductor device having highly reliable bonding portions can be obtained.

In addition, in the semiconductor device according to this second embodiment, the electrode terminal 6 is a flat plate, the root of the electrode terminal 6 is divided in the thickness direction or in the width direction.

According to the present embodiment, the root of the electrode terminal 6 in the shape of a flat plate is divided into two branches in the width direction. Accordingly, in fabrication of the electrode terminal 6, the root of the electrode terminal 6 can be divided into two branches by a press processing. Accordingly, a semiconductor device which is easily processed and reduced in cost can be obtained.

In addition, in the semiconductor device according to this second embodiment, the root of the electrode terminal 6 is divided into two, three, or four branches.

According to the present embodiment, the root of the electrode terminal 6 is divided into two branches. Accordingly, in this second embodiment, by dividing the root of the electrode terminal 6 into two branches, the current flowing in each terminal (branches 6 c, 6 d) is reduced by half, and thus the heating value of each of the bonding faces is reduced by half as compared to that of the first embodiment. This enables the thermal stress applied to each bonding face to be reduced by half.

In addition, in the semiconductor device according to this second embodiment, the branch parts at the root of the electrode terminal 6 are separated from each other toward the bonding faces 7 a, 7 b in a plan view.

In the semiconductor device according to this second embodiment, the branches 6 a, 6 b form an angle of 90° with each other in a plan view. Accordingly, peeling of the bonding faces 7 a, 7 b can be suppressed as compared to a case where the bonding face is provided only in one direction of the electrode terminal 6, even when a force to peel the electrode terminal 6 upward (stress generated perpendicular to the bonding face) is generated. Accordingly, a semiconductor device having highly reliable bonding portions can be obtained.

Third Embodiment

<Structure>

FIG. 4 is a perspective view of an electrode terminal 6 and a conductive pattern 4 b according to a third embodiment. In this third embodiment, the electrode terminal 6 is a flat plate. The root of the electrode terminal 6 is divided into two branches in the thickness direction. In other words, the root of the electrode terminal 6 includes two branches 6 a, 6 b.

As shown in FIG. 4, the branches 6 a, 6 b are bent in opposite directions to form an angle of 180° with each other in a plan view. The branch 6 a is bonded to the conductive pattern 4 b by ultrasonic bonding on the bonding face 7 a. Similarly, the branch 6 b is bonded by the ultrasonic bonding to the conductive pattern 4 b on the bonding face 7 b. Each of the branches 6 a, 6 b is bonded by the ultrasonic bonding to the conductive pattern 4 b at one position on one of the bonding faces 7 a, 7 b. The total sum of the areas of the bonding faces 7 a, 7 b according to this third embodiment is twice as large as that of the bonding face 7 according to the prerequisite art. The recesses 5 a, 5 b are formed by the ultrasonic bonding on the upper surfaces of the branches 6 a, 6 b, respectively. In this third embodiment, when the thickness of the electrode terminal 6 is defined as w6, the thickness of the branch 6 a is defined as w6 a, and the thickness of the branch 6 b is defined as w6 b, w6=w6 a+w6 b and w6 a=w6 b are satisfied. Note that w6 a and w6 b may be arbitrary values on condition that the thicknesses satisfy the relation, w6=w6 a+w6 b.

<Operation>

In this third embodiment, the sectional areas of the branches 6 a and 6 b of the electrode terminal 6 are assumed equal to each other. In this case, when the current flowing in one electrode terminal is defined as I [A], the current flowing in each of the branches 6 c, 6 d is I/2[A]. At the bonding faces 7 a, 7 b, the thicknesses of the branches 6 a, 6 b that are subjected to bonding are less than those in the second embodiment. With this structure, the stress applied to the branches 6 a, 6 b is reduced by half with respect to the mechanical stress due to the expansion of the electrode terminal 6.

<Effects>

In the semiconductor device according to this third embodiment, the electrode terminal 6 is a flat plate, and the root of the electrode terminal 6 is divided in the thickness direction or in the width direction.

In this third embodiment, the root of the electrode terminal 6 in the shape of a flat plate is divided into two branches in the thickness direction. Accordingly, since the thickness of the electrode terminal 6 is reduced at the bonding portions, the electrode is deformed largely due to the stress, and thus the stress applied to the bonding portions can be reduced and a semiconductor device having highly reliable bonding portions can be obtained.

In addition, in the semiconductor device according to this third embodiment, the root of the electrode terminal 6 is divided into two, three, or four branches.

According to this third embodiment, the root of the electrode terminal 6 is divided into two branches. Accordingly, in this third embodiment, by dividing the root of the electrode terminal 6 into two branches, the current flowing in each terminal (branches 6 c, 6 d) is reduced by half, and thus the heating value of each of the bonding faces is reduced by half as compared to that of the first embodiment. This enables the thermal stress applied to each bonding face to be reduced by half.

In addition, since two bonding faces 7 a, 7 b are provided by dividing the root of the electrode terminal 6 into two branches, peeling of the bonding faces 7 a, 7 b can be suppressed as compared to a case where one bonding face 7 is provided as in the prerequisite art, even when a force to peel the electrode terminal 6 upward (stress generated perpendicular to the bonding face) is generated. Accordingly, a semiconductor device having highly reliable bonding portions can be obtained.

In addition, in the semiconductor device according to this third embodiment, the branch parts at the root of the electrode terminal 6 are angled such that the branch parts go away from each other in a plan view with respect to the bonding faces 7 a, 7 b.

In the semiconductor device according to this third embodiment, the branches 6 a, 6 b form an angle of 180° with each other in a plan view. Accordingly, peeling of the bonding faces 7 a, 7 b can be suppressed as compared to a case where the bonding face is provided only in one direction of the electrode terminal 6, even when a force to peel the electrode terminal 6 upward (stress generated perpendicular to the bonding face) is generated. Accordingly, a semiconductor device having highly reliable bonding portions can be obtained.

Fourth Embodiment

<Structure>

FIG. 5 is a perspective view of an electrode terminal 6 and a conductive pattern 4 b according to a fourth embodiment. In this fourth embodiment, the electrode terminal 6 is a flat plate. The root of the electrode terminal 6 is divided into two branches in the width direction. In other words, the root of the electrode terminal 6 includes two branches 6 a, 6 b.

As shown in FIG. 5, the branches 6 a, 6 b are bent in opposite directions to form an angle of 180° with each other in a plan view. The branch 6 a is bonded to the conductive pattern 4 b by ultrasonic bonding on the bonding face 7 a. Similarly, the branch 6 b is bonded by the ultrasonic bonding to the conductive pattern 4 b on the bonding face 7 b. Each of the branches 6 a, 6 b is bonded by the ultrasonic bonding to the conductive pattern 4 b at one position on one of the bonding faces 7 a, 7 b. The recesses 5 a, 5 b are formed by the ultrasonic bonding on the upper surfaces of the branches 6 a, 6 b, respectively.

<Effects>

In addition, in the semiconductor device according to this fourth embodiment, the electrode terminal 6 is a flat plate, and the root of the electrode terminal 6 is divided in the thickness direction or in the width direction.

According to this fourth embodiment, the root of the electrode terminal 6 in the shape of a flat plate is divided into two branches in the width direction. Accordingly, in fabrication of the electrode terminal 6, the root of the electrode terminal 6 can be divided into two branches by a press processing. Accordingly, a semiconductor device which is easily processed and reduced in cost can be obtained.

In addition, in the semiconductor device according to this fourth embodiment, the root of the electrode terminal 6 is divided into two, three, or four branches.

According to this fourth embodiment, the root of the electrode terminal 6 is divided into two branches. Accordingly, in this fourth embodiment, by dividing the root of the electrode terminal 6 into two branches, the current flowing in each terminal (branches 6 c, 6 d) is reduced by half, and thus the heating value of each of the bonding faces is reduced by half as compared to that of the first embodiment. This enables the thermal stress applied to each bonding face to be reduced by half.

In addition, since two bonding faces 7 a, 7 b are provided by dividing the root of the electrode terminal 6 into two branches, peeling of the bonding faces 7 a, 7 b can be suppressed as compared to a case where one bonding face 7 is provided as in the prerequisite art, even when a force to peel the electrode terminal 6 upward (stress generated perpendicular to the bonding face) is generated. Accordingly, a semiconductor device having highly reliable bonding portions can be obtained.

In addition, in the semiconductor device according to this fourth embodiment, the branch parts at the root of the electrode terminal 6 are angled such that the branch parts go away from each other in a plan view with respect to the bonding faces 7 a, 7 b.

In the semiconductor device according to this fourth embodiment, the branches 6 a, 6 b form an angle of 180° with each other in a plan view. Accordingly, peeling of the bonding faces 7 a, 7 b can be suppressed as compared to a case where the bonding face is provided only in one direction of the electrode terminal 6, even when a force to peel the electrode terminal 6 upward (stress generated perpendicular to the bonding face) is generated. Accordingly, a semiconductor device having highly reliable bonding portions can be obtained.

Fifth Embodiment

<Structure>

FIG. 6 is a plan view and a front view of a structure of a semiconductor device according to a fifth embodiment. FIG. 7 is a perspective view of an electrode terminal 6 and a conductive pattern 4 b. Note that in FIG. 7, semiconductor elements (an MOSFET chip 2, an SBD chip 3) are omitted for easy understanding. As shown in FIG. 6, a plurality of conductive patterns 4 a, 4 b, 4 c are formed on the insulating substrate 1.

In this fifth embodiment, the electrode terminal 6 is a flat plate. The root of the electrode terminal 6 is divided into four branches. In other words, the root of the electrode terminal 6 includes four branches 6 a, 6 b, 6 c, 6 d. As shown in FIG. 7, opposing branches 6 a, 6 c are bent in directions that are opposite to each other. Similarly, opposing branches 6 b, 6 d are bent in directions that are opposite to each other. In other words, the branch 6 a and the branch 6 b, the branch 6 b and the branch 6 c, the branch 6 c and the branch 6 d, and the branch 6 d and the branch 6 a respectively form an angle of 90° with each other in a plan view.

The branches 6 a, 6 b, 6 c, 6 d are bonded to the conductive pattern 4 a by ultrasonic bonding on the bonding faces 7 a, 7 b, 7 c, 7 d, respectively. Each of the branches 6 a, 6 b, 6 c, 6 d is bonded by the ultrasonic bonding to the conductive pattern 4 a at one position on one of the bonding faces 7 a, 7 b, 7 c, 7 d. The recesses 5 a, 5 b, 5 c, 5 d are formed by the ultrasonic bonding on the upper surfaces of the branches 6 a, 6 b, 6 c, 6 d, respectively.

As shown in FIG. 6, an SBD chip 3 is bonded to the conductive pattern 4 a at a position next to the branch 6 a and the branch 6 b. In addition, an SBD chip 3 is bonded to the conductive pattern 4 a at a position next to the branch 6 b and the branch 6 c. In addition, an MOSFET chip 2 is bonded to the conductive pattern 4 a at a position next to the branch 6 c and the branch 6 d. An MOSFET chip 2 is bonded to the conductive pattern 4 a at a position next to the branch 6 d and the branch 6 a.

<Operation>

In the semiconductor device configured as shown in FIG. 6 and FIG. 7, when a semiconductor element comes into operation, a current flows into the electrode terminal 6 and then the electrode terminal 6 generates heat. In the case where there is a difference between the distances from each of the branches 6 a, 6 b, 6 c, 6 d to the MOSFET chips 2 and the SBD chips 3 when a power semiconductor element is in operation, the wiring resistance is varied depending on the distance, and thus the amounts of the current flow become unequal. This causes a deviation in the heating positions. Since the heat makes the whole electrode terminal 6 expand, a stress such as a tensile stress is applied to the root of the electrode terminal 6, which is a bonding portion, and thus a difference in the amount of the heating value generates a difference in the stress applied to the branches 6 a to 6 d.

According to this fifth embodiment, the branches 6 a to 6 d are disposed to extend in four directions, and the MOSFET chips 2 and the SBD chips 3 are disposed next to the branches, and thus a difference between the distances from each of the branches 6 a, 6 b, 6 c, 6 d to the MOSFET chips 2 and the SBD chips 3 can be reduced. With this structure, a deviation in the temperature rise caused by an uneven current flow can be reduced, and thus the heat cycle property is improved.

In addition, since the bonding faces 7 a to 7 d are provided in four directions of the electrode terminal 6, peeling of the bonding faces 7 a to 7 d can be suppressed as compared to a case where one bonding face 7 is provided as in the prerequisite art, even when a force to peel the electrode terminal 6 upward (stress generated perpendicular to the bonding face) is generated. Accordingly, a semiconductor device having highly reliable bonding portions can be obtained, and thus the heat cycle property is improved.

<Effects>

In the semiconductor device according to this fifth embodiment, the root of the electrode terminal 6 is divided into two, three, or four branches.

According to this fifth embodiment, the root of the electrode terminal 6 are divided into four branches, and the branches 6 a to 6 d are disposed to extend in four directions. The MOSFET chips 2 and the SBD chips 3 are disposed next to the branches, and thus a difference between the distances from each of the branches 6 a, 6 b, 6 c, 6 d to the MOSFET chips 2 and the SBD chips 3 can be reduced. With this structure, a deviation in the temperature rise caused by an uneven current flow can be reduced.

In addition, in the semiconductor device according to this fifth embodiment, the branch parts at the root of the electrode terminal 6 are angled such that the branch parts go away from each other in a plan view with respect to the bonding faces 7 a, 7 b.

In the semiconductor device according to this fifth embodiment, the branches 6 a, 6 b, 6 c, 6 d form an angle of 90° with each other in a plan view. Accordingly, peeling of the bonding faces 7 a, 7 b, 7 c, 7 d can be suppressed as compared to a case where the bonding face is provided only in one direction of the electrode terminal 6, even when a force to peel the electrode terminal 6 upward (stress generated perpendicular to the bonding face) is generated. Accordingly, a semiconductor device having highly reliable bonding portions can be obtained.

Sixth embodiment

<Structure>

FIG. 8 is a perspective view of an electrode terminal 6 and a conductive pattern 4 b of a semiconductor device according to a sixth embodiment. The semiconductor device may include the electrode terminal 6 according to this sixth embodiment instead of the electrode terminal 6 according to the fifth embodiment (FIG. 7).

The electrode terminal 6 according to this sixth embodiment is a flat plate, and the root thereof is divided into three branches. In other words, the root of the electrode terminal 6 includes three branches 6 a, 6 b, 6 c. As shown in FIG. 8, the branch 6 a and the branch 6 b, and the branch 6 b and the branch 6 c are bent to form an angle of 90° with each other in a plan view.

The branches 6 a, 6 b, 6 c are bonded to the conductive pattern 4 a by ultrasonic bonding on the bonding faces 7 a, 7 b, 7 c, respectively. Each of the branches 6 a, 6 b, 6 c is bonded by the ultrasonic bonding to the conductive pattern 4 a at one position on one of the bonding faces 7 a, 7 b, 7 c. The recesses 5 a, 5 b, 5 c are formed by the ultrasonic bonding on the upper surfaces of the branches 6 a, 6 b, 6 c, respectively.

As shown in FIG. 8, an SBD chip 3 is bonded to the conductive pattern 4 a at a position next to the branch 6 a and the branch 6 b. In addition, an SBD chip 3 is bonded to the conductive pattern 4 a at a position next to the branch 6 b and the branch 6 c. In addition, an MOSFET chip 2 is bonded to the conductive pattern 4 a at a position opposite to the SBD chip 3 across the branch 6 a. In addition, an MOSFET chip 2 is bonded to the conductive pattern 4 a at a position opposite to the SBD chip 3 across the branch 6 c.

Note that although each of the branch 6 a and the branch 6 b, the branch 6 b and the branch 6 c are bent to form an angle of 90° with each other in a plan view, they may be bent to form an arbitrary angle, for example an angle of 120°.

<Effects>

In the semiconductor device according to this sixth embodiment, the root of the electrode terminal 6 is divided into two, three, or four branches.

According to this sixth embodiment, the root of the electrode terminal 6 is divided into three branches, and the branches 6 a to 6 c are disposed to extend in three directions. The MOSFET chips 2 and the SBD chips 3 are disposed next to the branches, and thus a difference between the distances from each of the branches 6 a, 6 b, 6 c to the MOSFET chips 2 and the SBD chips 3 can be reduced. With this structure, a deviation in the temperature rise caused by an uneven current flow can be reduced, and thus the heat cycle property is improved.

In addition, since the bonding faces 7 a to 7 c are provided in three directions of the electrode terminal 6, peeling of the bonding faces 7 a to 7 c can be suppressed as compared to a case where one bonding face 7 is provided as in the prerequisite art, even when a force to peel the electrode terminal 6 upward (stress generated perpendicular to the bonding face) is generated. Accordingly, a semiconductor device having highly reliable bonding portions can be obtained.

In addition, in fabrication of the electrode terminal 6, the root of the electrode terminal 6 can be divided into three branches by a press processing. Accordingly, a semiconductor device which is easily processed and reduced in cost can be obtained.

In addition, in the semiconductor device according to this sixth embodiment, the branch parts at the root of the electrode terminal 6 are angled such that the branch parts go away from each other in a plan view with respect to the bonding faces 7 a, 7 b, 7 c.

In the semiconductor device according to this sixth embodiment, the branches 6 a, 6 b, 6 c form an angle of 90° with each other in a plan view. Accordingly, peeling of the bonding faces 7 a, 7 b, 7 c can be suppressed as compared to a case where the bonding face is provided only in one direction of the electrode terminal 6, even when a force to peel the electrode terminal 6 upward (stress generated perpendicular to the bonding face) is generated. Accordingly, a semiconductor device having highly reliable bonding portions can be obtained.

Seventh Embodiment

<Structure>

FIG. 9 is a perspective view of an electrode terminal 6 and a conductive pattern 4 b of a semiconductor device according to a seventh embodiment. In the semiconductor device according to this seventh embodiment, the electrode terminal 6 is bonded to the conductive pattern 4 b by ultrasonic bonding on one bonding face 7 in the same manner as the first embodiment (FIG. 1 and FIG. 2). This bonding face 7 includes two bonding portions. In other words, two recesses 5 a, 5 b are generated on the upper surfaces of the roots of the electrode terminal 6 at the time of the ultrasonic bonding.

In FIG. 9, the recess 5 a is formed at the time of the ultrasonic bonding in which a tool (see tool 13 in FIG. 14) is vibrated in the x-direction. In addition, the recess 5 b is formed at the time of the ultrasonic bonding in which the tool is vibrated in the y-direction. In other words, a plurality of positions subjected to the ultrasonic bonding on the bonding face 7 are vibrated in directions different from each other at the time of the ultrasonic bonding.

<Effects>

In the semiconductor device according to this seventh embodiment, with respect to the plurality of positions subjected to the ultrasonic bonding on the bonding face 7, vibration directions of the ultrasonic bonding are different from each other at the time of the ultrasonic bonding.

Accordingly, in this seventh embodiment, the vibration directions of the ultrasonic bonding are changed at each position subjected to the ultrasonic bonding and thus directions with weak bonding strength can be dispersed. In other words, the bonding face 7 that is bonded with more uniform strength can be obtained.

In addition, the vibration direction of the ultrasonic bonding is set to a direction different from the direction in which the insulating substrate 1 is vulnerable to vibration, and thus generation of a crack on an insulating substrate 1 can be avoided. In addition, the vibration direction of the ultrasonic bonding is set to a direction in which the electrode terminal 6 is susceptible to a thermal stress, and thus the bonding reliability improves.

Eighth Embodiment

<Structure>

FIG. 10 is a perspective view of an electrode terminal 6 and a conductive pattern 4 b of a semiconductor device according to an eighth embodiment. In the semiconductor device according to this eighth embodiment, the electrode terminal 6 is bonded to the conductive pattern 4 b by ultrasonic bonding on one bonding face 7 in the same manner as the first embodiment (FIG. 1 and FIG. 2). This bonding face 7 includes two bonding portions. Two recesses 5 a, 5 b are generated on the roots of the electrode terminal 6 at the time of the ultrasonic bonding. Here, the recess 5 b is formed inside the recess 5 a in a plan view. In other words, the ultrasonic bonding is performed twice in such a manner that a bonding portion of the second ultrasonic bonding is overlapped with that of the first ultrasonic bonding.

<Effects>

On the bonding face 7 of the semiconductor device according to the present embodiment, the ultrasonic bonding is performed a plurality of times in such a manner that positions subjected to the ultrasonic bonding are overlapped with each other in a plan view.

Accordingly, in this eighth embodiment, a plurality of bonding portions subjected to the ultrasonic bonding are provided on one bonding face 7 so as to overlap with each other, and thus a position in which the bonding strength is increased can be provided on the bonding face 7. For example, when an electrode terminal 1 is bonded to a surface including a vicinity of an end surface of the insulating substrate 1, a first ultrasonic bonding is performed with an energy that does not damage the insulating substrate 1, and then a second ultrasonic bonding is performed only around the center of the insulating substrate 1. This prevents the ultrasonic bonding from generating a crack on the insulating substrate 1, and enables obtaining a desired bonding strength.

Ninth Embodiment

<Structure>

FIG. 11 is a perspective view of an electrode terminal 6 and a conductive pattern 4 b of a semiconductor device according to a ninth embodiment. In addition, FIG. 12 is a sectional view taken along line AB in FIG. 11.

In this ninth embodiment, coining is performed at the root of the electrode terminal 6. As shown in FIG. 12, a depression 6 e is formed on the upper surface of the root of the electrode terminal 6 and at the same time, a projection 6 f is formed on the lower surface of the root of the electrode terminal 6 by the coining.

In addition, on the upper surface of an insulating substrate 1, a depression is provided at a position corresponding to the projection 6 f. This depression is formed by a mechanical processing or by an etching. Since the conductive pattern 4 b is formed on the surface of the insulating substrate 1, a depression 41 b is also formed on the conductive pattern 4 b at a position corresponding to the depression on the insulating substrate 1, as shown in FIG. 12.

In fabrication processes, firstly, the electrode terminal 6 is disposed on the conductive pattern 4 b. At this time, the projection 6 f of the electrode terminal 6 is engaged with the depression 41 b of the conductive pattern 4 b. Then, a tool is pressed against the upper surface of the electrode terminal 6, and the electrode terminal 6 is bonded to the conductive pattern 4 b by ultrasonic bonding. By the ultrasonic bonding, a recess 5 is formed on the upper surface of the root of the electrode terminal 6.

Note that although a projection is formed on the electrode terminal 6 and a depression is formed on the conductive pattern 4 b according to the present embodiment, the depression may be formed on the electrode terminal 6 and the projection may be formed on the conductive pattern 4 b to engage with the depression.

<Effects>

The semiconductor device according to this ninth embodiment includes the insulating substrate 1 on which the conductive pattern 4 b is formed, and an electrode terminal 6 and a semiconductor element that are bonded to the conductive pattern 4 b, the electrode terminal 6 and the conductive pattern 4 b are bonded by the ultrasonic bonding on a bonding face 7, the electrode terminal 6 includes a projection 6 f and the conductive pattern 4 b includes the depression 41 b on the bonding face 7, or the electrode terminal 6 includes a depression and the conductive pattern 4 b includes a projection on the bonding face, and the projection 6 f and the depression 41 b are engaged with each other.

In this ninth embodiment, the projection 6 f is engaged with the depression 41 b. Since the projection 6 f and the depression 41 b are engaged with each other before performing the ultrasonic bonding, the electrode terminal 6 is easily positioned with respect to the conductive pattern 4 b. This stables a relative position of the electrode terminal 6 and the conductive pattern 4 b at the time of the ultrasonic bonding, and thus the energy of the ultrasonic bonding can be sufficiently obtained. Since the ultrasonic bonding can be stably performed, a semiconductor device having a high bonding reliability can be obtained.

Tenth Embodiment

(Description of Structure)

FIG. 13 is a plan view of a semiconductor device according to a tenth embodiment, and a sectional view of the electrode terminal 6 and the conductive pattern 4 b.

The semiconductor device according to this tenth embodiment has the same structure as that of the first embodiment (FIG. 1, FIG. 2) except for the shape of a bonding face between the electrode terminal 6 and the conductive pattern 4 b.

A projection 6 g is formed on the lower surface of the root of the electrode terminal 6. In addition, a depression 42 b is formed on the surface of the conductive pattern 4 b. The projection 6 g has a shape that is engaged with the depression 42 b. For example, the projection 6 g is formed by mechanical processing, and the depression 42 b is formed by etching.

In a fabrication process, firstly, the electrode terminal 6 is formed on the conductive pattern 4 b. At this time, the projection 6 g of the electrode terminal 6 is engaged with the depression 42 b of the conductive pattern 4 b. Then, a tool is pressed against the upper surface of the electrode terminal 6, and the electrode terminal 6 is bonded to the conductive pattern 4 b by ultrasonic bonding. At this time, the ultrasonic bonding is performed at two positions. Two recesses 5 a, 5 b are formed on the upper surface of the root of the electrode terminal 6 by the ultrasonic bonding. In this tenth embodiment, the positions subjected to the ultrasonic bonding, the projection 6 g, and the depression 42 b overlap with each other in a plan view. In other words, two recesses 5 a, 5 b on the upper surface of the electrode terminal 6, the projection 6 g, and the depression 42 b overlap with each other in a plan view.

Note that in this embodiment, although a projection is formed on the electrode terminal 6 and a depression is formed on the conductive pattern 4 b, the depression may be formed on the electrode terminal 6, a projection may be formed on the conductive pattern 4 b to engage with each other. In addition, a plurality of the projections 6 g and a plurality of the depressions 42 b may be formed. In addition, a corner between the projection 6 g and the depression 42 b may be smooth.

<Effects>

In the semiconductor device according to this tenth embodiment, the projection 6 g and the depression 42 b overlap with the position subjected to the ultrasonic bonding in a plan view.

In this tenth embodiment, the projection 6 g is engaged with the depression 42 b. The projection 6 g and the depression 42 b are engaged with each other before performing the ultrasonic bonding, and thus the electrode terminal 6 is easily positioned with respect to the conductive pattern 4 b. With this structure, the relative position of the electrode terminal 6 and the conductive pattern 4 b are stabled at the time of the ultrasonic bonding, and the energy of the ultrasonic bonding can be sufficiently obtained. In addition, since the depression and the projection are provided at a position subjected to the ultrasonic bonding on the bonding face, the area of the bonding face can be increased, and thus the bonding strength can be increased. In view of the above, a semiconductor device having a high bonding reliability can be obtained.

In addition, in the semiconductor device according to this tenth embodiment, the ultrasonic bonding is performed at a plurality of positions.

Accordingly, the area of each of the bonding portions can be reduced. Therefore, an absolute value of a thermal stress at each of the bonding portions can be reduced, peeling of the bonding face 7 can be suppressed. In addition, since the total area of the bonding portions is increased, a highly reliable semiconductor device can be obtained.

Although this invention is described in detail, the above descriptions are examples in all aspects, and this invention is not limited to that extent. Unlimited number of modifications that are not exemplified can be estimated without deviating from the scope of this invention.

REFERENCE SIGNS LIST

1: insulating substrate,

2: MOSFET chip

3: SBD chip

4 a, 4 b, 4 c: conductive pattern

5, 5 a, 5 b, 5 c, 5 d: recess

6: electrode terminal

6 a, 6 b, 6 c, 6 d: branch

7, 7 a, 7 b, 7 c, 7 d: bonding face

8: bonding member

9: sealing member

10: outsert case

11: base plate

12: adhesive agent

13: tool

14: metal wire. 

1. A semiconductor device comprising: an insulating substrate on which a conductive pattern is formed; and an electrode terminal and a semiconductor element that are bonded to the conductive pattern, wherein the electrode terminal and the conductive pattern are bonded together by ultrasonic bonding through at least one bonding face, and the ultrasonic bonding is performed at a plurality of positions.
 2. The semiconductor device according to claim 1, wherein the at least one bonding face is one bonding face, and the ultrasonic bonding is performed at a plurality of positions on the one bonding face.
 3. The semiconductor device according to claim 1, wherein the at least one bonding face is a plurality of bonding faces, a root of the electrode terminal is divided, the divided root forms the plurality of bonding faces, and each of the plurality of bonding faces includes at least one position subjected to the ultrasonic bonding.
 4. The semiconductor device according to claim 3, wherein the electrode terminal is a flat plate, and the root of the electrode terminal is divided in the thickness direction or in the width direction.
 5. The semiconductor device according to claim 3, wherein the root of the electrode terminal is divided into two, three, or four branches.
 6. The semiconductor device according to claim 4, wherein the root of the electrode terminal is divided into two, three, or four branches.
 7. The semiconductor device according to claim 3, wherein branch parts at the root of the electrode terminal are angled such that the branch parts go away from each other in a plan view with respect to the bonding faces.
 8. The semiconductor device according to claim 4, wherein branch parts at the root of the electrode terminal are angled such that the branch parts go away from each other in a plan view with respect to the bonding faces.
 9. The semiconductor device according to claim 2, wherein with respect to the plurality of positions on the bonding face subjected to the ultrasonic bonding, vibration directions of the ultrasonic bonding are different from each other.
 10. The semiconductor device according to claim 1, wherein the ultrasonic bonding is performed a plurality of times in such a manner that the positions on the bonding face subjected to the ultrasonic bonding are overlapped with each other in a plan view.
 11. A semiconductor device comprising: an insulating substrate on which a conductive pattern is formed; and an electrode terminal and a semiconductor element that are bonded to the conductive pattern, wherein the electrode terminal and the conductive pattern are bonded together by ultrasonic bonding through at least one bonding face, the electrode terminal includes a projection and the conductive pattern includes a depression on the bonding face, or the electrode terminal includes a depression and the conductive pattern includes a projection on the bonding face, and the projection and the depression are engaged with each other.
 12. The semiconductor device according to claim 11, wherein the projection and the depression are overlap with the position subjected to the ultrasonic bonding in a plan view.
 13. The semiconductor device according to claim 12, wherein the ultrasonic bonding is performed at a plurality of positions. 